6.3.7 CustomMetaDataProperties Property

DataSetMetaData describe the content and the semantics of a DataSet. Subscribers use this metadata to interpret the DataSet from the DataSetMessage and can evaluate the Properties field of the FieldMetaData Structure (see OPC 10000-14).

The CustomMetaDataProperties Property contains an array of KeyValuePairs. The purpose of this Property is the enhancement of the DataSetMetaData if the SerializedData Variable is serialized in a PubSub scenario. If the SerializedData Variable is used in a published DataSet, the KeyValuePairs of the CustomMetaDataProperties Property shall be added to the Properties field in the FieldMetaData Structure representing the SerializedData Variable in the containing DataSetMetaDataType Structure comprising the DataSetMetaData (see OPC 10000-14).

The field names from the structures containing the Values the semantic Properties belong to are qualified with the OPC UA Namespace. This allows the encoder to omit the NamespaceIndex when serializing the QualifiedName inside the KeyValuePair.

Figure 10 shows the structure of the CustomMetaDataProperties for a SerializationScope excluding the metadata comprising the EUInformation and EngineeringUnits Properties of the AnalogUnitType and AnalogUnitRangeType Variables in the SerializationScope.

image013.png

Figure 10 – CustomMetaDataProperties example

The content of the CustomMetaDataProperties Property of the SerializedData Variable describes the semantic Properties for all Values mapped into the SerializationValue DataType of the SerializedData. It is used as Properties field of the FieldMetaData Structure representing the SerializedData Variable in the DataSet.

The KeyValuePair elements at the lowest indices contain the semantic Properties (e.g. key=“EngineeringUnits”, value=EUInformation) for the Value of the represented Variable. Sub-Variables are represented with elements containing KeyValuePairs with keys equal to the BrowseNames of the Variables (see “Variable1”, “Variable2” and “Variable3” elements) and arrays of KeyValuePairs for the semantic Properties of those Variables as values.